Welcome

The title says it all: this blog features physics videos found everywhere on the web: animations, demonstrations, lectures, documentaries.

Please go here if you want to suggest other nice physics videos, and here if I mistakingly infringed your copyrights. If you understand French, you'll find a huge selection of physics videos in French in my other blog Vidéos de Physique.

Sungrazing Comet ISON, expected to become a bright naked-eye object later this year, might dust the Earth with meteoroids in early 2014. Researchers discuss the possibilities in this week's ScienceCast.

Monday, 15 April 2013

The world's roundest object helps solve the longest running problem in measurement -- how to define the kilogram.
A kilogram isn't what it used to be. Literally. The original name for it was the 'grave', proposed in 1793 but it fell victim to the French Revolution like its creator, Lavoisier. So begins the tale of the most unusual SI unit. The kilogram is the only base unit with a prefix in its name, and the only one still defined by a physical artifact, the international prototype kilogram or IPK.

But the problem with this definition has long been apparent. The IPK doesn't seem to maintain its mass compared to 40 similar cylinders minted at the same time. The goal is therefore to eliminate the kilogram's dependence on a physical object. Two main approaches are being considered to achieve this end: the Avogadro Project and the Watt Balance.

The Avogadro project aims to redefine Avogadro's constant (currently defined by the kilogram -- the number of atoms in 12 g of carbon-12) and reverse the relationship so that the kilogram is precisely specified by Avogadro's constant. This method required creating the most perfect sphere on Earth. It is made out of a single crystal of silicon 28 atoms. By carefully measuring the diameter, the volume can be precisely specified. Since the atom spacing of silicon is well known, the number of atoms in a sphere can be accurately calculated. This allows for a very precise determination of Avogadro's constant.

Special thanks to Katie Green, Dr. David Farrant, the CSIRO, and the National Measurment Institute for their help. Thanks also to Nessy Hill for filming and reviewing earlier drafts of this video.

Tuesday, 2 April 2013

MAVEN's dual magnetometers will allow scientists to study the interaction between the solar wind and the Martian atmosphere, giving us a better understanding of how Mars has evolved from a warm, wet climate to the cold, arid one we see today.

Monday, 1 April 2013

A comet is heading for Mars, and there is a chance that it might hit the Red Planet in October 2014. An impact wouldn't necessarily mean the end of NASA's Mars program. But it would transform the program along with Mars itself.